Compressive strength and regional supply implications of rice straw and rice hull ashes used as supplementary cementitious materials

• The availability of lower GHG emission supplementary cementitious materials in the U.S. needs to be increased. • Rice straw ash as a supplementary cementitious material can reach similar strengths as Portland cement-only binders. • Potential rice straw ash supply is twice that of rice hull ash and, in some U.S. regions, is large compared to Portland cement use. • Overall, rice biomass ash could replace large amounts of regionally used cement in the U.S. to help reduce GHG emissions. • Rice biomass ashes could also be an important GHG-reducing supplementary cementitious material in other rice-growing countries. Substituting Portland cement (PC) with supplementary cementitious materials (SCMs) is a key strategy for reducing greenhouse gas (GHG) emissions. Considering alternative SCMs requires a holistic understanding of changes to material performance, emissions reduction potential, and regional availability. Four rice hull ashes (RHAs) and one rice straw ash (RSA) were evaluated to replace PC in mortars (10% untreated ash and 30% blast furnace slag; 15% untreated ash; or 15% milled ash). The 28-day compressive strengths with 0.59 water-to-binder ratio for fly-RHAs (38.0–49.8 MPa) and RSA (37.7 - 44.1 MPa) did not vary significantly from the PC control (43.2 MPa) based on an ANOVA. Modeling rice biomass generation in six U.S. states shows RSA could triple the supply of rice-biomass ash, but in states with substantial PC demand, i.e., California and Texas, the potential GHG reduction may remain small (∼1–2%). RSA and RHA may hold promise in lowering concrete GHG emissions.